biology

Microvascular decompression

Microvascular decompression is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Microvascular decompression rather than just read about it. In short: Microvascular decompression (MVD), also known as the Jannetta procedure, is a neurosurgical procedure used to treat trigeminal neuralgia (along with other cranial nerve neuralgias), a pain syndrome characterized by severe episodes of intense facial pain, and hemifacial spasm. The procedure is also used experimentally to treat tinnitus and vertigo caused by vascular compression on the vestibulocochlear nerve.

Key takeaways

Microvascular decompression belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Microvascular decompression to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Microvascular decompression from memory before moving on to harder problems.

Reference excerpt

Microvascular decompression (MVD), also known as the Jannetta procedure, is a neurosurgical procedure used to treat trigeminal neuralgia (along with other cranial nerve neuralgias), a pain syndrome characterized by severe episodes of intense facial pain, and hemifacial spasm. The procedure is also used experimentally to treat tinnitus and vertigo caused by vascular compression on the vestibulocochlear nerve. As the goal of the Jannetta procedure is to relieve (vascular) pressure on the trigeminal nerve, it is a specific type of a nerve decompression surgery.

History Nicholas Andre first described trigeminal neuralgia in 1756. In 1891 Sir Victor Horsley proposed the first open surgical procedure for the disorder involving the sectioning of preganglionic rootlets of the trigeminal nerve. Walter Dandy in 1925 was an advocate of partial sectioning of the nerve in the posterior cranial fossa. During this procedure he noted compression of the nerve by vascular loops, and in 1932 proposed the theory that trigeminal neuralgia was caused by compression of the nerve by blood vessels, typically the superior cerebellar artery. With the advent of the operative microscope, Peter J. Jannetta was able to further confirm this theory in 1967 and advocated moving the offending vessel and placing a sponge to prevent the vessel from returning to its native position as a treatment for trigeminal neuralgia.

Patient selection Patients most likely to benefit from a microvascular decompression have a classic form of trigeminal neuralgia. The diagnosis of this disorder is on the basis of the patients' symptoms and from a neurological examination. No blood test or genetic marker exists to diagnose the disease. An MRI scan can help eliminate other diagnoses. Newer MRI techniques may allow for the visualization of vascular compression of the nerve. Patients who improve with an MVD are likely to have pain which is episodic rather than constant. The pain typically has an electrical quality to it and is intense. The pain can usually be triggered. Common triggers include light touch, eating, talking or putting on make-up. Most patients whose face pain improved with an MVD also improved at least temporarily with medication. In addition to having the proper type of pain, candidates for an MVD must also be healthy enough to undergo surgery. The risk of surgery may increase with increasing patient age.

Surgical technique

Patients are put to sleep using general anaesthesia and are positioned on their back with their head turned or on their side with the symptomatic side facing up. Electrical monitoring of facial function and hearing is used. A straight incision is made two finger-breadths behind the ear about the length of the ear. A portion of the skull around 30 mm (1.2 inches) in diameter is removed exposing the underlying brain covering known as the dura. The dura is opened to expose the cerebellum. The cerebellum is allowed to fall out of the way exposing the side of the brainstem. Using a microscope or endoscope and micro-instruments, the arachnoid membrane is dissected allowing visualization of the 8th, 7th and finally the trigeminal nerve. The offending loop of blood vessel is then mobilized. Frequently a groove or indentation is seen in the nerve where the offending vessel was in contact with the nerve. Less often the nerve is thin and pale. Once the vessel is mobilized a sponge like material is placed between the nerve and the offending blood vessel to prevent the vessel from returning to its native position. After the decompression is complete, the wound is flushed clean with saline solution. The dura is closed in a watertight fashion. The skull is reconstructed and the overlying tissues are closed in multiple layers. The patient is allowed to wake up and is taken to an intensive care unit or other close observation unit.

Results The largest reported series of MVDs was reported by Jannetta and published in The New England Journal of Medicine in 1996. The initial success rate was 82% for complete relief with an additional 16% having partial relief for a combined initial success rate of 98%. At 10 year follow-up, 68% had excellent or good relief. 32% had recurrent symptoms. Other series report similar or better results.

Complications Serious complications from an MVD include death (0.1%), stroke (1%), hearing loss (3%) and facial weakness (0.5%). Dr. Jannetta has called facial paralysis (as opposed to weakness) a "major and common complication of the MVD." (2 separate depositions under oath: Levy v Jannetta, CCP Allegheny County, GD 81–7689.) Other complications include leakage of spinal fluid and wound infection (1%). Most patients will have transient neck pain and stiffness from the surgical incision and from seeding of the spinal fluid with small amounts of blood.

Other procedures Several other surgical procedures exist for the treatment of trigeminal neuralgia, including percutaneous rhizotomy, percutaneous glycerol injection, percutaneous balloon compression, rhyzotomy and stereotactic radiosurgery (SRS). When compared to the other procedures, MVD carries the highest long-term success rate, but it also carries the highest risk.

Worked examples

Example 1 — a first encounter with Microvascular decompression

Start with the simplest possible case. Write down what Microvascular decompression claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Microvascular decompression before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Microvascular decompression ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Microvascular decompression

In research: Microvascular decompression appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Microvascular decompression in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Microvascular decompression is common in secondary-school and first-year university syllabi. It links to neighbouring topics Neurosurgery, so understanding it makes those chapters shorter.
In everyday life: Look for Microvascular decompression outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Microvascular decompression in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Microvascular decompression means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Microvascular decompression out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Microvascular decompression in simple terms?

Why does Microvascular decompression matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Microvascular decompression?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Microvascular decompression.